In the field of electrical circuits, manufacture of dielectric laminates and microwave circuit performance, temperature stability of the dielectric constant (TCK) is an important parameter. The dielectric constant of high dielectric ceramics changes with temperature. As a result, the effective dielectric constant of the composites comprising of polymer and ceramic filler also changes with temperature. The change in temperature during circuit operation affects the electrical properties of electronic components utilizing the compositions, such as, for example, the operating frequency of a patch antenna. This may limit the usefulness of the electronic devices, since they are only usable within limited temperature ranges. In particular, the Outdoor use may be unreliable.
This problem has so far been tried to be addressed by several prior arts which disclose compositions of polymer filled with more than one particulate ceramic material to control the temperature coefficient of dielectric constant (TCK). This approach is described in U.S. Pat. No. 5,358,775 wherein a high dielectric constant (K≧4), low temperature coefficient of dielectric constant (TCK≦150 ppm/° C.) electrical substrate material comprising a fluoropolymer filled with Class 1 capacitor material such as barium neodymium titanate together with secondary fillers such as silica and alumina is disclosed. The same approach is extended in U.S. Pat. No. 5,552,210 wherein, a high dielectric constant (K≧5) and comparatively low thermal coefficient (TCK<200 ppm/° C.) polymeric composite matrix is disclosed using particulate fillers such as titania, magnesia, alumina etc. incorporated in the fluoropolymeric matrix to tune the dielectric properties. Further, high capacitance laminates made of thin films comprising polytetrafluoroethylene filled with large amounts of dielectric filler (25 to 85 vol %), in which the films are plated or clad with conductive material are disclosed in U.S. Pat. No. 4,996,097. The high dielectric fillers which are used include TiO2, BaTiO3 or a Ferro-electric complex.
Temperature stable substrate materials have also been developed in the ceramic filled non-fluoropolymeric based systems which is disclosed in U.S. Pat. No. 5,223,568 wherein, a ceramic filler blend comprising of barium nonotitanate and silica is incorporated in the poly(1,2-butadiene) liquid resin.
A polymer composition having high dielectric constant has been disclosed in U.S. Pat. No. 5,739,193 which is made from poly (phenylene sulfide) (PPS), a thermoplastic polymer, filled with strontium titanate, barium neodymium titanate, barium strontium titanate/magnesium zirconate etc. as primary fillers and mica as the secondary filler material. In addition, a polymeric composition having a dielectric constant K>4 at 20° C. which varies little with temperature is disclosed in U.S. Pat. No. 5,965,273 wherein, the polymeric composition is made from a polymer or mixture of polymers and a ceramic or a mixture of ceramics where the polymer or mixture of polymers have K in the range of about 1.5 to about 3.5 and TCK which is negative and is between 0 and about −300 ppm/° C. The polymer is selected from a group consisting of poly(phenylene sulfide), cycloolefinic copolymer and mixtures thereof filled with a first ceramic filler material consisting of calcium zirconate, strontium zirconate, CaTiSiO5, PbZrO3, zirconia and mixtures thereof, each having dielectric constant in the range of about 15 to about 200 and TCK>0 up to about 300 ppm/° C. and an optional second ceramic filler comprising of one or more ceramic selected from the group consisting of aluminum oxide, magnesium titanate, mica, silicon dioxide, beryllia, spinel and thoria each having a dielectric constant in the range of about and a TCK>0 up to about 300 ppm/° C. However, the use of secondary fillers which is used to control the TCK of the composite system often adversely affects fine control over dielectric constant, homogeneity, rheology etc. of the composite systems. This is the reason as to why such temperature stable high dielectric thermoplastic composite systems (comprising secondary fillers) are not available in the open market for commercial use.
Hence, there is still a need for better and improved electrical composite substrates which possess extraordinary properties such as high dielectric constant, low dielectric loss and low temperature coefficient of dielectric constant.
The present disclosure aims at overcoming all the aforesaid drawbacks of the prior art.